You only learned the technical side of things. you need to also learn the semantic side of it. Its like painting, you may know how to paint a pretty face, a nice sunset, but what is the message? Without a message, a painting is a mere demonstration of how well you hold your paintbrush and not much else.
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GaptonMar 5 '12 at 13:49

That's true. Well, for me is important to have sound techincal ability in order to communicate something (so this is why I want to study some subjects). What do you suggest about the semantic side? I like arts in general, but honestly most of the time I enjoy things without seeing any inspiration :)
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PaoloMar 5 '12 at 13:56

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Try shooting a project with a theme. For example loneliness. How do you convey loneliness in a series of photos? Thinking about these questions will enhance your ability to embed a message in your photographs.
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GaptonMar 6 '12 at 6:51

But it sounds like you're mostly focusing on book learnin'. A book will never make you step up in your photographic skills without the practice to go along with it. It's really easy to read a lot of books and hang out on web sites without putting in the work — but putting in the work is what will produce the results. Malcom Gladwell, author of The Tipping Point, has an interesting theory that it takes roughly 10,000 hours of anything to become an expert. Put in time towards those hours.

As you take photographs, come back and take a look at the results with a critical eye. Think about what worked and what didn't. Choose your best few every month, even when it's hard to narrow things down. That self-critical process is a very effective tool. If you have two similar photographs that you can't choose between, make yourself choose one. Make some actual prints. Show people. (Don't get too hung up on web-forum "critique", though!) A local photography club might be useful, or it might not. The important thing is to make photographs, and to look at them. Don't get caught up in the secondary aspects (although you can do those too — that's basically what this site is).

Then, as you do that, you will come to specific things for which you realize you need to turn to expert advice and historical wisdom. That's when you look in a book, or ask a question here. You'll almost certainly discover that your understanding of even the basic concepts can go to whole new levels.

I do not think my answer is going to be comprehensive. I will try to answer based on my own experience.

Light and Lighting

Light is the most important component in a photograph. It is also the difference between a plain boring picture and an inspiring, dramatic picture. One book that will always find space in my bookshelf would be Light Science and Magic. The book explains concepts using artificial light but the concept remains the same and can be used in any type of photography. I can quote from the book:

Learn about the light and science. The magic will happen.

Photography the art

Science of photography is easy, art behind is not. Two books that I can recommend to understand and develop art behind photography are:

Apart from knowing a bit about aperture and exposure and so forth, make sure you know how to use your camera. Can you change exposure without taking your eye off the viewfinder? Do you know how to dial in exposure compensation. Do you understand all the different metering or autofocus options on your camera, what situations to use them, and how to quickly change them? If not, pick one thing per week, read the manual, then experiment. Only when the technical stuff is second nature will you be able to forget all about that and be creative without being distracted by fumbling with menus and settings.

To work on creative side of things, and push those boundaries of your technical knowledge, I'd suggest:

Besides rule of thirds, research other compositional elements, and go out and take shots which exploit things like

negative space

color contrast

leading lines

patterns and texture

balance

Try different types/styles of photography - each will give you new challenges and things to learn:

do some portraits - work on lighting, post processing perhaps

landscapes - work on composition, DOF

abstract - composition, shapes, textures

try some black and white conversions - shoot some images with B&W in mind

street photography

product or still life - bowl of fruit or some jewelry

motion - sports or birds in flight, work on focus, panning technique

night photography - handheld multi-second exposures

golden hour - sunrise/sunset

get in close, very close if you have a macro lens

experiment with focus, DOF

Carry your camera with you every day. Every day take at least a few shots of something you see. Can be an ordinary thing, but try not to take an ordinary snapshot - try an interesting perspective or angle, convert it to B&W, do something to make it special.

Go some place like your kitchen or garden. Take 50 photos. Experiment with focus, perspective, exposure. Review these and see what you like. Do it again, same place. Another 50. Keep at it, you'll start to unlock some creativity.

As mattdm said, as you go, keep a portfolio of your best shots. I don't consider myself that great, but I've been doing this as a hobby for 30 years, and what pleases me is my best shots are always some of my most recent ones, so I know I'm still improving.

To be honest, at the beginning of my photography journey, I got myself two books from the library, read them, but didn't find them as interesting and inspiring as some simple articles I found on internet later.

Since then I always get inspiration and practical tips from photography websites.
As for product photography, joining stock agencies helped me a lot, it "trained" me to produce good quality images and become a disciplined photographer.

Flickr was very helpful when I was learning to use flashes, because many people (me too) put description of light set up and camera settings under their photos.

As the last note I want to mention that photography demands lots and lots of practice in order to develop skills and achieve good results. Hope it helps ;)

Just as an aside since you mentioned Photoshop and lighting as areas of possible interest, Lightroom might be a good thing to look into. Simply put it is lighting editing tool much like Photoshop. I was really impressed by the newest version and what it can do. It seems a very good fit for more technical skills you could learn.